Week of April 18, 2021

Mon Apr 19, 2021
4:00pm to 5:50pm - Zoom - Logic Set Theory
Eric Mjolsness - (UC Irvine)
What does logic have to do with AI/ML for computational science?

Progress in artificial intelligence (AI), including machine learning (ML),
is having a large effect on many scientific fields at the moment, with much more to come.
Most of this effect is from machine learning or "numerical AI", 
but I'll argue that the mathematical portions of "symbolic AI" 
- logic and computer algebra - have a strong and novel roles to play
that are synergistic to ML. First, applications to complex biological systems
can be formalized in part through the use of dynamical graph grammars.
Graph grammars comprise rewrite rules that locally alter the structure of
a labelled graph. The operator product of two labelled graph
rewrite rules involves finding the general substitution 
of the output of one into the input of the next - a form of variable binding 
similar to unification in logical inference algorithms. The resulting models
blend aspects of symbolic, logical representation and numerical simulation.
Second, I have proposed an architecture of scientific modeling languages
for complex systems that requires conditionally valid translations of
one high level formal language into another, e.g. to access different
back-end simulation and analyses systems. The obvious toolkit to reach for
is modern interactive theorem verification (ITV) systems e.g. those
based on dependent type theory (historical origins include Russell and Whitehead).
ML is of course being combined with ITV, bidirectionally.
Much work remains to be done, by logical people.
 

This is part 1 of a 2 part talk. It will cover background on:
Sketch of background knowledge in typed formal languages, 
Curry-Howard-Lambek correspondence, 
current computerized theorem verification, ML/ITV connections;
scientific modeling languages based on rewrite rules
(including dynamical graph grammars),
with some biological examples.

Thu Apr 22, 2021
9:00am to 10:00am - Zoom - Inverse Problems
Ting Zhou - (Northeastern University)
Inverse Problems for Nonlinear PDEs

https://sites.uci.edu/inverse/

10:00am to 11:00am - zoom https://uci.zoom.us/j/93076750122?pwd=Y3pLdndoQTBuNUhxQUxFMkQ2QnRFQT09 - Mathematical Physics
Milivoje Lukic - (Rice University)
Reflectionless canonical systems: almost periodicity and character-automorphic Fourier transforms

This talk describes joint work with Roman Bessonov and Peter
Yuditskii. In the spectral theory of self-adjoint and unitary
operators in one dimension (such as Schrodinger, Dirac, and Jacobi
operators), a half-line operator is encoded by a Weyl function; for
whole-line operators, the reflectionless property is a
pseudocontinuation relation between the two half-line Weyl functions.
We develop the theory of reflectionless canonical systems with an
arbitrary Dirichlet-regular Widom spectrum with the Direct Cauchy
Theorem property. This generalizes, to an infinite gap setting, the
constructions of finite gap quasiperiodic (algebro-geometric)
solutions of stationary integrable hierarchies. Instead of theta
functions on a compact Riemann surface, the construction is based on
reproducing kernels of character-automorphic Hardy spaces in Widom
domains with respect to Martin measure. We also construct unitary
character-automorphic Fourier transforms which generalize the
Paley-Wiener theorem. Finally, we find the correct notion of almost
periodicity which holds in general for canonical system parameters in
Arov gauge, and we prove generically optimal results for almost
periodicity for Potapov-de Branges gauge, and Dirac operators.

3:00pm - Zoom https://uci.zoom.us/j/99706368574 - Number Theory
Remy van Dobben de Bruyn - (IAS/Princeton University)
A variety that cannot be dominated by one that lifts.

The recent proofs of the Tate conjecture for K3 surfaces over finite fields start by lifting the surface to characteristic 0. Serre showed in the sixties that not every variety can be lifted, but the question whether every motive lifts to characteristic 0 is open. We give a negative answer to a geometric version of this question, by constructing a smooth projective variety that cannot be dominated by a smooth projective variety that lifts to characteristic 0.

Fri Apr 23, 2021
3:00pm to 4:00pm - Zoom (notice unusual day) - Applied and Computational Mathematics
Marco Donatelli - (Università dell'Insubria, Como (Italy))
Preconditioning strategies for iterative soft-thresholding algorithms
Zoom
We explore the use of a regularizing preconditioner for a modification of the linearized Bregman iteration applied to the image deblurring problem with a 1-norm regularization term in the wavelet domain. Motivated by the nonstationary preconditioned iteration introduced in [1] for least-square inverse problems, we propose a new algorithm that combines this method with the linearized Bregman algorithm [2]. The proposed preconditioning strategy improves the quality of the restored images and saves some computational cost with respect to the standard preconditioning employed in the modified linearized Bregman algorithm [3] and a numerical comparison with similar methods, like FISTA, is presented. We prove that it is a regularizing and convergent method. A variant with a structure preserving preconditioner is also considered [4].

Research partly carried out with D. Bianchi, A. Buccini, Y. Cai, M. Hanke, T.Z. Huang.

[1] M. Donatelli, M. Hanke, Fast nonstationary preconditioned iterative methods for ill-posed problems, with application to image deblurring, Inverse Problems, 29 (2013) 095008.
[2] Y. Cai, M. Donatelli, D. Bianchi, T.Z. Huang, Regularization preconditioners for frame-based image deblurring with reduced boundary artifacts, SIAM J. Sci. Comput., 38--1 (2016), pp. B164--B189.
[3] J.F. Cai, S. Osher, Z. Shen, Linearized {B}regman iterations for frame-based image deblurring, SIAM J. Imaging Sci., 2--1 (2009), pp. 226--252.
[4] D. Bianchi, A. Buccini, M. Donatelli, Structure Preserving Preconditioning for Frame-Based Image Deblurring, Springer INdAM Series, 36 (2019), pp. 33--49.